Jewelry identification and testing has long been a challenge in the human history. The challenges, among others, are mainly to identify if a target test piece contains certain desirable alloys, and if so, the concentration and thickness of each of them, and further if the desirable elements are present in the bulk of the test piece or are merely plated on the surface of the test piece.
In the last few decades, x-ray florescence (XRF) technologies have been more often used for jewelry analysis. XRF is now a widely used, proven, and accepted method of chemistry analysis and used in karating of precious metals samples, including for purity and fineness. XRF analysis provides a less expensive, quicker testing alternative to fire assay and chemical tests, and on-the-spot analysis of silver, platinum, or other materials, making it an easy way to boost customer confidence and ensure dealer reliability.
However, a method and instrument for accurate and fast identification of whether a piece of jewelry is plated with certain precious metal has seen lagging the market needs. The challenges remain due to a few considerations, among them, the need to address deviating standard of thickness or cut-off threshold for defining whether a piece of jewelry is plated or not. For example, the thickness of identified gold on the surface of necklace in a range of 5 to 10 micron would render the conclusion that the necklace is gold plated. However, for bracelets, the same thickness of 5 to 10 microns might not render the same conclusion that the bracelets are gold-plated.
Some prior teachings shown to use XRF for measuring concentrations of certain elements, in surface-covering layers, such as paint, can be found with reference to U.S. Patents, for example, U.S. Pat. Nos. 5,396,529 and 7,702,067, both by Grodzins, (herein collectively as “Grodzins”). Grodzins teaches measurement of the concentration of lead in paint on the basis of inducing and detecting fluorescence of the x-rays of lead.
The contents of the foregoing Grodzins U.S. Pat. Nos. 5,396,529 and 7,702,067 are incorporated herein by reference.
The previous teachings as mentioned above all include the following steps using XRF for identifying a specified element on the surface of an object:                a. illuminating a surface of the sample with x-ray excitation radiation;        b. measuring a first intensity of a characteristic emission line of the specified element at a first energy;        c. measuring a second intensity of a characteristic emission line of the specified element at a second energy;        d. calculating the ratio between the first intensity to the second intensity to establish the possible thickness of the specified element disposed above the bulk of the sample.        
It therefore can be understood that the thickness can be quite accurately measured in existing practice as discussed above. However, existing methods do not address sufficiently what the measured thickness should be compared to, in order to obtain a confident conclusion whether the sample is to be considered plated with the precious metal or not. A predetermined cut-off thickness threshold to determine whether the sample meets the criterion qualifying the sample to be considered to be plated needs to be further defined for each functional category, i.e., chains, bracelets; and for each types of metal, i.e., silver, gold, etc. Therefore, an improved method and instrument is needed to more accurately and confidently provide customers with a reliable indication and/or quantitative measure indicative of whether a piece of jewelry is plated with the desirable metal or is not.